2.1. Parkinson's Disease
Despite enormous therapeutic advances, Parkinson's disease (PD) continues to be one of the most common causes of disability in the elderly. In patients with typical Parkinson's disease, the results of magnetic resonance imaging are usually normal. However, when a high field strength, heavily T2 weighed magnetic resonance imaging is used, a wider area of lucency in the substantia nigra is seen, indicative of increased accumulation of iron. In general, iron in the substantia nigra area has been reported in many publications as being causative of or at least contributory to the development of Parkinson's disease.
Iron is known to be a catalyst for the fenton reaction, by which the generation of reactive oxygen free radicals occurs. Iron is typically found within cells in the iron storage molecule ferritin. Once stored in ferritin, iron is generally unavailable as a catalyst for the production of free radicals.
Research has been focused on the MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine toxin) model of Parkinson's disease based on the advances in the neuropathology and neurochemistry of the disease. This toxin selectively damages the dopaminergic neurones of the substantia nigra when oxidized to MPP+. Anti-oxidants prevent the oxidation of MPTP to MPP+ and have been investigated clinically for the treatment of Parkinson's disease. It has been also postulated that endogenous or exogenous toxins, including metabolites of dopamine, generate hydroxyl radicals and hydrogen peroxide, which are known neurotoxic substances. These toxins interfere with normal mitochondrial metabolism. Abnormalities have also been reported in the complex I (NADH:ubiqinone oxidoreductase).